Polymerization of cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene and other substituted cyclohexadienes

ABSTRACT

The monomer cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene can be polymerized with certain nickel II catalysts, such as bis[(ally)trifluoroacetatonickel(II)], bis[(allyl)pentafluorophenoxynickel(II)], and bis[(allyl)iodonickel(II)]. The resulting polymer is a precursor to poly(para-phenylene). Other substituted cyclohexadienes may also be polymerized by these catalysts to form useful polymers.

ORIGIN OF INVENTION

The U.S. Government has rights in this invention pursuant to ContractNo. AFOSR-88-0094, awarded by the Department of the Air Force.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part application of Ser.No. 07/647,576, filed Jan. 29, 1991, allowed.

TECHNICAL FIELD

The present invention relates to the polymerization ofpoly(para-phenylene), and, more particularly, to the preparation of aprecursor thereto.

BACKGROUND ART

Poly(para-phenylene) (PPP) is a fully aromatic, rigid rod polymer withunique structural and conductive properties. As an engineering plastic,its attractiveness arises from its thermal stability (mp >500° C.), highstrength, chemical inertness, and solvent resistance. When doped witheither n- or p-type dopants, the polymer forms highly conducting chargetransfer complexes with conductivities up to 500 S/cm. However, thestructural properties which make PPP so attractive also make it adifficult polymer to synthesize. In addition, many of the observedproperties of the polymer depend on the method of production.

Previous methods of producing PPP directly have met with only limitedsuccess. For example, oxidative cationic polymerization of benzene toproduce PPP has been attempted. However, only short oligomers of ten tofifteen repeat units containing mixtures of linear 1,4- and non-linear1,2-units were formed.

Polymerizations using nickel catalyzed aryl coupling of1,4-dihalobenzenes were attempted. While this method produced acompletely linear molecule, only short oligomers consisting of ten totwelve units were formed.

The problem with these direct synthetic methods is that the inherentinsolubility of the polymer causes it to precipitate out of solutionbefore high molecular weight materials can be formed. Electrochemicalcoupling of benzene has also been used, but the resulting film isinsoluble and composed of a mixture of 1,4- and 1,2-linked units.

In order to circumvent the problem of the inherent insolubility of PPPin production and processing, soluble precursor methodologies have beendeveloped. For example, polymers of 1,3-cyclohexadiene (CHD) have beenused as a soluble precursor polymer. In particular, poly(cyclohexadiene)has been reacted with bromine and then pyrolyzed to eliminate HBr.Unfortunately, this polymerization route also produces a precursorpolymer with a mixture of 1,4- and 1,2-linkages. In addition, theelimination reaction is not very efficient, since HBr readily reactswith unsaturated intermediates.

Recently, the efficient production of PPP has been reported, via thepyrolysis of a soluble precursor polymer prepared from the radicalpolymerization of the acetyl and methoxycarbonyl derivatives of5,6-dihydroxy-1,3-cyclohexadiene (DHCD); see, e.g., D. G. Ballard et al,Macromolecules, Vol. 21, pp. 294-304 (1988) and D. R. McKean,Macromolecules, Vol. 20, pp. 1787-1792 (1987). The starting cis-diol isproduced by the microbial oxidation of benzene. The precursor films aresoluble and can be processed before pyrolysis to the final polymer.However, the radical polymerization produces about 85% 1,4-linked unitsand 15% 1,2-linked units. The 1,2-units create "kinks" in the polymer,there-by reducing the elimination efficiency of the precursor and themechanical properties of the final polymer.

In order for the good mechanical properties of PPP to be realized, anaspect ratio of at least 100 consecutive linear 1,4-units per 1,2-unitmust be obtained. All previous routes to PPP have either produced lowmolecular weight materials due to insolubility of the growing polymer,or have incorporated a significant amount of 1,2-linkages in the chains,or both. Hence, it is desirable to find an exclusively1,4-polymerization method which can be used in combination with theefficient precursor method described above.

DISCLOSURE OF INVENTION

In accordance with the invention,cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene is polymerized in thepresence of a nickel(II) catalyst having an allyl group and a nonbasicelectron withdrawing ancillary ligand; examples includebis[(allyl)trifluoroacetatonickel(II)],bis[(allyl)pentafluorophenoxynickel(II)], andbis[(allyl)iodonickel(II)]. This novel polymer is suitably employed as aprecursor to PPP.

More specifically, the polymer that is formed,1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene) or1,4-poly(TMS-CHD), is converted to the corresponding diacetoxy polymer,1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene) or 1,4-poly(DA-CHD), byreacting with acetyl chloride in the presence of zinc chloride or ferricchloride. To ensure 100% acetylation, the 1,4-poly(DA-CHD) is retreatedwith an excess of pyridine and either acetic anhydride or acetylchloride.

The polymer 1,4-poly(TMS-CHD) is also converted to fully acetylated1,4-poly(DA-CHD) by deprotection of the trimethylsiloxy groups tohydroxy groups, such as by using a fluoride source. The resultinghydroxy polymer, 1,4-poly(cis-5,6-dihydroxy-1,3-cyclohexadiene) or1,4-poly(DH-CHD), is then treated with pyridine and either aceticanhydride or acetyl chloride to yield the fully acetylated1,4-poly(DA-CHD).

The fully acetylated 1,4-poly(DA-CHD) is then converted topoly(para-phenylene) by the pyrolysis reaction with loss of acetic acid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b depict the 1,4- and 1,2-linkages ofpoly(para-phenylene), respectively;

FIG. 2 depicts the polymerization ofcis-5,6-bis(tri-methylsiloxy)-1,3-cyclohexadiene (TMS-CHD);

FIG. 3a depicts the structure of bis[(allyl)trifluoroacetatonickel(II)](ANiTFA)₂ ;

FIG. 3b depicts the structure ofbis[(allyl)pentafluorophenoxynickel(II)];

FIG. 3c depicts the structure of bis[(allyl)iodonickel(II)];

FIG. 4, on coordinates of percent polymer yield and monomerconcentration (molar), is a plot of the dependence of polymer yield as afunction of monomer concentration for the TMS-CHD system, with themonomer-to-catalyst ratio=80:1, where the catalyst isbis[(allyl)trifluoroacetatonickel(II)];

FIG. 5, on coordinates of percent polymer yield and ratio of monomer tocatalyst, is a plot of the dependence of polymer yield as a function ofthe monomer-to-catalyst ratio for the system of FIG. 4;

FIG. 6 depicts the conversion of1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene) to1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene);

FIG. 7 depicts the thermal conversion of1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene) to poly(para-phenylene);

FIG. 8a, on coordinates of signal strength and chemical shift relativeto tetramethyl silane, is the 500 MHz ¹ H NMR spectrum of poly(TMS-CHD)prepared with the catalyst (ANiTFA)₂ ;

FIG. 8b, on the same coordinates as FIG. 8b, is the 500 MHz ¹ H NMRspectrum of radically polymerized poly(TMS-CHD) for comparison;

FIGS. 9a and 9b are the comparative 400 MHz ¹ H NMR spectra ofpoly(DA-CHD) made by radical polymerization and from poly(TMS-CHD),respectively;

FIG. 10a is the IR spectrum of poly(cis-5,6-diacetoxy-1,3-cyclohexadiene(poly(DA-CHD)) prepared by prior art radical polymerization;

FIG. 10b is the IR spectrum of poly(DA-CHD) prepared from1,4-poly(TMS-CHD) prior to the retreatment step of the invention;

FIGS. 11a and 11b are the comparative powder X-ray data for poly(DA-CHD)made by radical polymerization and from poly(TMS-CHD), respectively;

FIG. 12 is the differential scanning calorimetry profile of1,4-poly(DA-CHD) made from poly(TMS-CHD);

FIG. 13, on coordinates of weight percent and temperature in °C., is athermogravimetric profile for 1,4-poly(DA-CHD) made from1,4-poly(TMS-CHD);

FIG. 14 depicts the reaction scheme of 1,4-poly(DA-CHD) retreatment inaccordance with the invention;

FIG. 15, on coordinates of signal strength and chemical shift relativeto tetramethyl silane, is the 500 MHz ¹ H NMR spectrum of fullyacetylated 1,4-poly(DA-CHD);

FIG. 16a is the IR spectrum of 1,4-poly(DA-CHD) prior to the retreatmentstep of the invention;

FIG. 16b is the IR spectrum of 1,4-poly(DA-CHD) subsequent to theretreatment step of the invention;

FIG. 17 is the differential scanning calorimetry profile of fullyacetylated 1,4-poly(DA-CHD);

FIG. 18 depicts the reaction scheme of 1,4-poly(DA-CHD) production via1,4-poly(DH-CHD);

FIG. 19 is the powder X-ray diffraction pattern of fully acetylated1,4-poly(DA-CHD);

FIG. 20a, on coordinates of signal strength and chemical shift relativeto tetramethyl silane, is the 400 MHz ¹ H NMR spectrum of theacetoxy-polymer available from ICI Chemicals and Polymers, UnitedKingdom;

FIG. 20b, likewise on coordinates of signal strength and chemical shiftrelative to tetramethyl silane, is the 400 MHz ¹ H NMR spectrum of 100%acetylated 1,4-poly(DA-CHD);

FIG. 21 is the optimum stereochemistry for acetic acid elimination from1,4-poly(DA-CHD);

FIG. 22 illustrates the comparative acetic acid elimination kinetics;

FIG. 23 is the IR spectrum of poly(para-phenylene) obtained frompyrolysis of fully acetylated 1,4-poly(DA-CHD);

FIG. 24 is the powder X-ray diffraction pattern of crystalline PPP; and

FIG. 25 is the aromatization kinetics of fully acetylated1,4-poly(DA-CHD) at 305° and 310° C.

BEST MODES FOR CARRYING OUT THE INVENTION

The 1,4- and 1,2-linkages of poly(para-phenylene) (PPP) are depicted inFIGS. la and lb, respectively. It is desired to produce PPP havingessentially 100% 1,4-linkages, which is defined herein as at least about96%. The process of the invention results in PPP having such linkages.The essentially 100% 1,4-linkages achieved in accordance with theinvention is considerably higher than that achieved in the prior art;PPP prepared by prior art processes typically includes 10 to 15%1,2-linkages.

The reaction sequence for polymerizingcis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene (TMS-CHD) is shown inFIG. 2. The polymerization is achieved, preferably using a nickelcatalyst having an oxidation state of two, an allyl group, and anon-basic, electron-withdrawing ligand. Examples of such catalystsinclude: bis[(allyl)trifluoroacetatonickel(II)] (ANiTFA)₂),bis[(allyl)pentafluorophenoxynickel(II)], andbis[(allyl)iodonickel(II)]. The structures for these three catalysts aregiven in FIGS. 3a, 3b, and 3c, respectively.

Bis[(allyl)trifluoroacetatonickel(II)] (ANiTFA)₂ is known to polymerize1,3-butadiene to exclusively 1,4-polybutadiene (PBD). The cis/transratio of the poly(butadiene) produced, as well as other properties suchas molecular weight, depend on the solvent system used duringpolymerization and the presence of electron donating or acceptingadditives.

Although (ANiTFA)₂ has been thoroughly studied with butadiene, it hasnot been used with cyclic 1,3-dienes or in the presence of heteroatomfunctionalities. This catalyst has never, at least to Applicants'knowledge, homopolymerized a heteroatom-substituted diene, or a cyclicdiene. It has only been used to copolymerize a heteroatom-substituteddiene with butadiene. Also, transition metal catalysts used for dienepolymerization are generally not compatible with heteroatomfunctionalities, and there has not been a demand for poly-cyclic dienesor functionalized PBD. Only the elastomers and thermoplastics of PBDhave been in demand. The usefulness of functionalized dienes (especiallyfor PPP synthesis) has only been recently discovered.

For polymerizing cyclic monomers, the cis/trans geometry is of noconcern, since the ring will always adopt a cisoid diene configuration.Only the 1,4- vs. 1,2-regiochemistry is important, and whether thecatalyst is compatible with polar functionalities.

To determine the possible use of (ANiTFA)₂ in polymerizing thetrimethylsiloxy-substituted cyclohexadiene, the polymerization of1,3-cyclohexadiene (CHD) using this catalyst was studied. A small amountof white, insoluble poly(cyclohexadiene) (PCHD) powder was produced,which indicated that (ANiTFA)₂ can polymerize a cyclic diene system.However, owing to the polymer's insolubility, the 1,4- vs. 2- contentcould not be determined.

Working under the assumptions that the efficiency of the reaction waslimited by either the insolubility of the growing chains or the catalystactivity's solvent dependence, the effect of various solvents on thesystem was studied. The results are listed in Table I, below.

                  TABLE I                                                         ______________________________________                                        Solvent Trends on CHD Polymerization.                                         Solvent         % Yields  Polymer Properties                                  ______________________________________                                        (neat)          27.1      insoluble                                           n-heptane        4.7      insoluble                                           benzene         11.2      sol., >90% 1,4                                      chlorobenzene   31.3      insoluble                                            -o-dichlorobenzene                                                                           66.7      insol., crystalline                                  -o-dichlorobenzene/BHT                                                                       55.5      insol., crystalline                                 ______________________________________                                    

Further purification of the monomer prior to reaction made isolatedyields up to 88.4% possible. Clearly, the more polar solvents producehigher polymer yields. This appears to be a solvent effect on thecatalyst, since in all cases, the polymer produced was insoluble inthese solvents. Only in the case of benzene was a small fraction of theresulting polymer soluble enough for NMR analysis.

By comparing the ratio of the integrals of the ¹ H NMR signals at 1.6and 2.0 ppm, the soluble fraction of the PCHD sample was determined tobe approximately 95% 1,4-linked. Gel permeation chromatography (GPC) ofthe soluble fraction revealed that the chains are only comprised of tento eleven monomer units with a polydispersity index (PDI) of 1.78.

The 1,4-regiochemistry of the polymers produced was also supported bythe fact that the insoluble polymers were crystalline. Wide angle,powder X-ray diffraction on the polymers showed sharp diffraction linescorresponding to lattice spacings similar to those observed forcrystalline terphenyl and PPP.

Differential scanning calorimetry (DSC) revealed that the crystallinePCHD was thermally stable up to 320° C. This value is over 100° C.higher than the PCHD samples produced by one prior art technique,involving Ziegler catalysts (TiCl₄) and cationic polymerization ofbenzene (D. A. Frey et al, Journal of Polymer Science, Part A, Vol. 1,p. 2057-2065 (1963)), and slightly higher than those made with a similarcatalyst, bis[(allyl)iodonickel(II)], whose composition was reported tobe >90% 1,4-linked. Endotherms at 367° C. and approximately 510° C. werealso observed for this polymer. It is not clear what these endothermsare due to; decomposition and glass transitions are possibilities.

(ANiTFA)₂ can also be used in o-dichlorobenzene to polymerize5-alkyl-1,3-cyclohexadienes, as can the catalystbis[(allyl)pentafluorophenoxynickel(II)]. These alkyl-substituted PCHDpolymers have interesting properties and may be useful in the future ascomonomers. These polymers appear to be soluble materials which can beused in high temperature environments (due to their high thermalstability), as exemplified by 5-methyl-1,3-cyclohexadiene. Other alkylgroups include neo-pentyl. The process for forming these alkylcyclohexadienes works with any 1,3-cyclohexadiene with pure hydrocarbonchains on the 5 and/or 6 positions on the ring.

Reaction of the acetyl derivative ofcis-5,6-dihydroxy-1,3-cyclohexadiene (DHCD) with (ANiTFA)₂ did notproduce any polymers, nor did the reaction of the methoxycarbonylderivative. Analysis of the resulting reaction mixture in each caserevealed that most of the monomer remained intact, but the catalystdecomposed to a green solid reminiscent of an inorganic nickel salt.

However, a 1:1 ratio of 1,3-cyclohexadiene (CHD) andbis(methoxycarbonyl)-1,3-cyclohexadiene (BMC-CHD) in benzene did producea copolymer in low yields. The product was a soluble white powder whose¹ H NMR spectrum clearly showed a signal at 3.75 ppm due to incorporatedmethoxycarbonyl functionalities. The effect of various solvents on thispolymerization system was studied as in the case of PCHD; the resultsare tabulated in Table II, below.

                  TABLE II                                                        ______________________________________                                        Solvent Trends on a 1:1 Feed Ratio of                                         CHD and BMC-CHD.                                                              Solvent               % Yield                                                 ______________________________________                                        (neat)                1.5                                                     benzene               1.5                                                     toluene               0.4                                                     chlorobenzene         2.3                                                      -o-dichlorobenzene   4.5                                                     ______________________________________                                    

In all cases, a 1:1 ratio of the two monomers produced polymers whichwere completely soluble. GPC analysis indicated that the products shouldbe considered short oligomers rather than polymers.

Once the best solvent for the system was determined to beortho-dichlorobenzene (o-DCB), a study to determine how differentmonomer feed ratios would affect the polymer yields and properties wasundertaken. The results are summarized in Table III.

                  TABLE III                                                       ______________________________________                                        Feed Ratio Trends on Copolymerization                                         in  -o-DCB.                                                                   CHD           BMC-CHD       % Yield                                           ______________________________________                                         0            100            0                                                 1             10            1.6                                               1             4             2.4                                               1             2             2.6                                               1             1             4.5                                               2             1             3.5                                               4             1             5.8                                               10            1            13.2                                              100            0            66.7                                              ______________________________________                                    

While greater BMC-CHD to CHD ratios greatly reduce the polymer yieldsdue to catalyst deactivation, they also increase the solubility of thepolymer due to greater methoxycarbonyl monomer incorporation in thepolymer.

The conclusion that can be drawn from the foregoing is that use of theacetyl and methoxycarbonyl derivatives of DHCD with (ANiTFA)₂ does notprovide a better route to a PPP precursor. Functional groupincompatibility with the catalyst is the most likely reason. Thisassumption was confirmed by adding various amounts of acarbonyl-containing compound (ethyl acetate; EtOAc) to a typical CHDpolymerization reaction. The results are shown in Table IV, below.

                  TABLE IV                                                        ______________________________________                                        Effect of Ethyl Acetate on CHD                                                Polymerization.                                                               Catalyst    EtOAc      CHD       % Yield                                      ______________________________________                                        1            0         470       66.7                                         1            4         470       19.7                                         1           470        470        2.5                                         ______________________________________                                    

The most plausible explanations for these functional groupincompatibilities are (1) that the polar carbonyl group can coordinateto the catalyst open site, thereby causing deactivation, or (2) thatester exchange reactions occur to give an inert nickel species whenother ester-like groups are present. Another possibility for themonomers' incompatibility may be that the catalyst facilitatesaromatization, as in the case of CHD, and the acidic side products ofthis reaction (ROH) destroy the catalyst.

Cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene (TMS-CHD) was preparedfrom cis-DHCD and reacted with (ANiTFA)₂. The polymerization of TMS-CHDwith (ANiTFA)₂ in chlorobenzene has been optimized, and the percentyields show dependencies on the concentration of TMS-CHD andmonomer-to-catalyst ratio, FIGS. 4 and 5, respectively. There, it isseen that the polymer yield is at least about 80% for a monomerconcentration of at least about 0.9 Molar (monomer-to-catalystratio=80:1) and that the polymer yield is at least about 80% for amonomer-to-catalyst ratio in the range of about 50:1 to 150:1. Higherratios may be used, providing the increased viscosity that accompaniessuch higher ratios is taken into account, such as by monomer dilution.

The lower limit of the TMS-CHD concentration is about 0.14 Molar; belowthis value, no polymer is formed. The optimum TMS-CHD concentration isabout 1.5 Molar, which gives 93% isolated yield of polymer with amonomer:catalyst ratio of 80:1 (FIG. 4).

TMS-CHD has an oxygen-containing group which is relativelynon-coordinating compared to carbonyl groups. Also, the monomer is lesssusceptible to aromatization, since TMS-OH is a relatively poor leavinggroup upon elimination in comparison to the acetate or carbonate groups.

Polymerization of this monomer with (ANiTFA)₂ was possible in a varietyof aromatic solvents to give a soluble white powder which was suitablefor GPC analysis. The results are listed in Table V, below.

                  TABLE V                                                         ______________________________________                                        Polymerization of TMS-CHD in Various                                          Aromatic Solvents.                                                                         Polymer                                                          Solvent      Yield     Mn       Mw     PDI                                    ______________________________________                                        benzene      13%        5667     6910  1.22                                   chlorobenzene                                                                              56        21466    37882  1.76                                    -o-dichlorobenzene                                                                        24        24245    41495  1.71                                   ______________________________________                                    

The effect of solvent polarity on this system was different than withprevious monomers. Although the catalyst is generally more active inmore polar aromatic solvents, the polymer itself is more soluble innon-polar solvents. With chlorobenzene, which is betweeno-dichlorobenzene and benzene in terms of polymer chain solubility andcatalytic enhancement, optimum yields were obtained. The polymerizationwas also performed in a 1:1 v/v solution of o-DCB and benzene. Theisolated polymer yields were similar to those obtained withchlorobenzene. As can be seen in Table V, the molecular weights (Mw) aresimilar and correspond to average degrees of polymerization of 85 to 90.Isolated yields up to 93% are possible if the monomer concentration isincreased, and the monomer is further purified by filtration throughalumina.

The properties exhibited by poly(TMS-CHD) make it a promising precursorpolymer to PPP. FIG. 6 depicts the conversion of poly(TMS-CHD) to thecorresponding acetoxy derivative, while FIG. 7 depicts the conversion ofthe acetoxy derivative to PPP. This latter conversion is known in theart, as evidenced by the Ballard reference cited above.

Poly(TMS-CHD) is a novel polymer and is soluble in a variety ofrelatively non-polar organic solvents such as benzene, toluene,chlorobenzene, hexanes, THF, ether, chloroform, and methylene chloride.In highly polar solvents such as o-DCB, acetonitrile, alcohols, andwater, the polymer is completely insoluble. Although the polymerprecipitates out of solution as a fine white powder, it can also formcolorless, clear, brittle, glassy films.

The regiochemistry of the poly(TMS-CHD) appears to be almost entirely1,4-linked, as determined by ¹ H NMR analysis. In particular, it isexpected that the presence of 1,2-units in similar polymers would bemanifested as a proton signal in the 1.8 to 2.1 ppm range. There is, infact, an absence of polymer proton signals in this region of thespectrum for poly(TMS-CHD). In contrast, radical polymerization ofTMS-CHD only produced short oligomers with a distinct ¹ H NMR signal at1.9 ppm due to 1,2-linkages (cf. FIGS. 8a and 8b).

Powder X-ray diffraction data provided further evidence that thepoly(TMS-CHD) polymer is entirely 1,4-linked and linear.

Conversion of 1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene)to 1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene) (1,4-poly(DA-CHD) wasaccomplished by two methods. The first method involved the addition ofacetyl chloride to a stirred solution of 1,4-poly(TMS-CHD) and anhydrouszinc chloride or iron (III) chloride, as illustrated in FIG. 6.

This initial procedure yielded 1,4-poly(DA-CHD) with approximately 96%acetoxy functionalities and about 4% hydroxy sidegroups, as revealed bythe signal at 3.9 ppm in its ¹ H NMR signal (FIG. 9b) and the O--Hstretch at 3470 cm³¹ 2 in its infrared spectrum (FIG. 10b). The 96%acetylated 1,4-poly(DA-CHD) was further characterized by powder X-raydiffraction (FIG. 11b), differential scanning analysis (DSC) (FIG. 12),and thermogravimetric analysis (TGA) (FIG. 13). FIGS. 9a, 10a, and 11ashow the NMR signal, infrared spectrum, and powder X-ray diffractogram,respectively, of the poly(DA-CHD) made by radical polymerization, andare included for comparison purposes.

Retreatment of the 96% acetylated polymer with excess pyridine andeither acetic anhydride or acetyl chloride yielded the 100% acetylated1,4-poly(DA-CHD) (FIG. 14). The absence of the proton signal at 3.9 ppmand the overall narrowing of all the polymer proton signals in the ¹ HNMR spectrum illustrates the complete acetylation (FIG. 15). As well,examination of the IR spectra of the 1,4-poly(DA-CHD) before and afterretreatment shows a dramatic reduction in the O--H absorbance at ≈3500cm⁻¹, which is due to residual hydroxy groups (FIGS. 16a and 16b).

The 100% acetylated 1,4-poly(DA-CHD), when compared to the original 96%acetylated polymer, also shows subtle differences by differentialscanning calorimetry (DSC). The shoulder transition at ≈295° C. on theDSC of the 96% acetylated polymer (FIG. 12) is absent in that ofretreated 1,4-poly(DA-CHD) (FIG. 17).

It is believed that this endotherm is not a glass transition (asoriginally thought), but rather an elimination endotherm due to theresidual hydroxy groups. Comparison of molecular weights by gelpermeation chromatography of the 1,4-poly(DA-CHD) before and afterretreatment revealed it to be unchanged.

The fully acetylated 1,4-poly(DA-CHD) could also be obtained from1,4-poly(TMS-CHD) by a second process. This second process involved thedeprotection of the trimethylsiloxy groups on the 1,4-poly(TMS-CHD) tohydroxy groups, using a fluoride source, such as tetra-butyl ammoniumfluoride, and an alcohol. Potassium fluoride with crown ethers and anyammonium salt of fluorine may also serve as a fluoride source. Thedeprotection reaction can also be accomplished by use of a stronganhydrous acid, such as anhydrous HCl in methanol. While thedeprotection reaction is a well-known reaction, it has been utilized inthe past primarily on monomeric materials; it has not been efficientlyused before on polymers, because performing quantitative substitution onpolymers is difficult to do. In the present reaction, 100% acetylationis observed, with almost quantitative isolated yields.

The resulting hydroxy-polymer, 1,4-poly(1,3-cyclohexadiene)[1,4-poly(DH-CHD)], was then treated with pyridine and either aceticanhydride or acetyl chloride to yield the fully acetylated1,4-poly(DA-CHD) (see FIG. 18). The 1,4-poly(DA-CHD) obtained by thisroute is virtually identical in terms of ¹ H NMR and IR spectroscopy andDSC analysis, to the 100% acetylated 1,4-poly(DA-CHD) obtained by thefirst method. The 100% acetylated 1,4-poly(DA-CHD) made by both methodsis amorphous, as revealed by X-ray diffraction (FIG. 19).

The fully acetylated 1,4-poly(DA-CHD) made by the two afore-mentionedmethods is intrinsically different from that made using a radicalinitiator in the prior art. Comparative ¹ H NMR spectroscopy andelimination kinetics of the 100% acetylated 1,4-poly(DA-CHD) made from1,4-poly(TMS-CHD) and the poly(DA-CHD) made by radical polymerizationshow marked differences. These differences have their origins in theregular stereo- and regiochemistry of the (ANiTFA)₂ catalyzed1,4-poly(TMS-CHD).

In contrast, the radically polymerized poly(DA-CHD) has a randomstereochemistry across the cyclohexadienyl repeat units, in addition tohaving about 10 to 15% 1,2-units. These differences are manifested inthe fully acetylated 1,4-poly(DA-CHD) having much sharper and moresymmetric signals in the ¹ H NMR spectrum (compare FIGS. 20a and 20b);even though GPC analysis revealed that the polymer made by the processof the invention is about one-half the molecular weight of that made bythe radical process.

The difference in stereoregularity between the two polymers is alsoevident in the kinetics of their acetic acid elimination processes (FIG.7). The prior art has revealed that the acetic acid elimination processfor PPP formation proceeds through a six-membered ring transition statein which the optimum stereochemistry is such that the acetate group andthe proton to be eliminated are in a cis arrangement on the ring (FIG.21). If the 1,4-poly(DA-CHD) made by the process of the invention hasthis optimum stereochemistry for facile acetic acid loss, then it shouldproceed faster than that made by the radical process, which has a randomstereochemistry. Indeed, this was observed to be the case (FIG. 22).Curve 22a represents the kinetics of acetic acid elimination for1,4-poly(DA-CHD) made by the process of the invention, while Curve 22brepresents the kinetics for 1,4-poly(DA-CHD) made by radicalpolymerization.

This evidence suggests that the fully acetylated 1,4-poly(DA-CHD) madefrom 1,4-poly(TMS-CHD) is intrinsically different from the radicallypolymerized poly(DA-CHD). (It should be noted here that all comparativedata herein were performed with a sample of radically polymerizedpoly(DACHD) provided by ICI Chemicals and Polymers, United Kingdom.)

As previously mentioned, the fully acetylated 1,4-poly(DA-CHD) could beconverted to poly(para-phenylene) with loss of acetic acid when heatedunder inert atmosphere in the solid state. Temperatures in the range ofabout 270° to 340° C. were used, although careful heating between 300°and 310° C. gave the best solid state pyrolysis results.

The poly(para-phenylene) so formed is a black flaky powder or a shinyblack film with a UV/visible absorption maximum at about 310 nm and astrong IR absorbance at 808 cm⁻¹ (FIG. 23). Through careful control ofthe heating conditions, the poly(para-phenylene) can either be amorphousor crystalline (FIG. 24). UV/visible and IR spectroscopy and X-raydiffraction are generally used to characterize poly(para-phenylene), andthe values herein compare favorably to those given in the prior art.

FIG. 25 shows typical aromatization kinetics data for the pyrolysis ofthe fully acetylated 1,4-poly(DA-CHD) at 305° C. (Curve 25a) and at 310°C. (Curve 25b).

In summary, (ANiTFA)₂ and related allyl-nickel catalysts can polymerizederivatives of 1,3-cyclohexadiene in a 1,4-fashion, so long as thefunctional groups do not coordinate to the catalyst, or are not easilyeliminated. The trimethylsiloxy derivative is compatible with thesecatalysts. The resulting polymer appears to be entirely 1,4-linked. Itis soluble in non-polar solvents and ordered in the solid state. Thepolymer can be easily converted by two methods to another precursorpolymer which is pyrolyzed to form poly(para-phenylene), as describedabove.

INDUSTRIAL APPLICABILITY

Poly(TMS-CHD) can be converted to1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene), which has been shown inthe prior art to be a precursor to poly(para-phenylene). The resultinghigh regioselectivity (substantially 100% 1,4-linkages) results inhighly improved mechanical properties of the final polymer. Further, thecatalysts bis[(allyl)trifluoroacetatonickel(II)],bis[(allyl)pentafluorophenoxynickel(II)], andbis[(allyl)iodonickel(II)]may be employed to polymerize substitutedcyclohexadienes.

EXPERIMENTAL General Considerations

All manipulations of air- and/or water-sensitive compounds wereperformed using conventional high vacuum or Schlenk techniques. Argonwas purified by passage through columns of BASF R3-11 catalyst (Chemlog)and 4 Å molecular sieves (Linde). Solid organometallic compounds andorganic monomers were transferred and stored in a nitrogen filled VacuumAtmospheres drybox. NMR spectra were recorded on a JEOL GX-400 (399.95MHz ¹ H, 100.40 MHz ¹³ C spectrometer. Infrared spectra were recordedwith a Perkin-Elmer 1600 series FT-IR spectrometer. Gel permeationchromatograms were obtained on a Waters 150C ALC/GPC using toluene at aflow rate of 1.0 ml/min and a column temperature of 35° C.; or on acustom system consisting of three Styragel columns, an Altex Model 110Apump, and a Knauer differential refractometer using methylene chlorideas the eluant at a flow rate of 1.5 ml/min at room temperature. PowderX-ray diffraction studies were performed on a Guinier camera with acamera constant of 0.358278 deg/mm or a Scintag diffractometer, usingCuKα radiation. Differential scanning calorimetry was performed on aPerkin-Elmer DSC-7, and thermogravimetric analysis was performed on aPerkin-Elmer TGS-2.

Pentane, n-heptane, benzene, diethyl ether, THF, and DME were vacuumtransferred from sodium benzophenone ketyl. Methylene chloride wasvacuum transferred from P₂ O₅. Chlorobenzene was distilled, dried overmolecular sieves, and filtered through activated alumina.Ortho-dichlorobenzene was distilled from calcium hydride at 20 Torr.Pyridine and triethylamine were both distilled from calcium hydride.Chlorotrimethylsilane was distilled from magnesium filings. Allyltrifluoroacetate was prepared by refluxing allyl alcohol andtrifluoroacetic acid in a Dean-Stark apparatus and purified bydistillation. 1,3-Butadiene was purified by condensation of the gas ontocalcium hydride at -78° C., and degassed by repeated freeze-pump-thawcycles. 1,3-Cyclohexadiene was distilled from sodium borohydride.Cis-5,6-dihydroxy-1,3-cyclohexadiene was obtained from Aldrich Chemicaland recrystallized from ethyl acetate and pentane prior to use. Theacetyl and methoxycarbonyl derivatives were obtained from ICI and usedas was. All monomers were stored in anhydrous, sub-zero conditions.

All distillations were performed under argon. All solvents and liquidreagents were degassed by repeated freeze-pump-thaw cycles and storedunder argon in Kontes flasks. Solid phase reagents and monomers weredegassed in vacuo and stored in the drybox prior to use.

Preparation of (ANiTFA)₂ Catalyst

1.00 g (3.64 mmol) of Ni(1,4-cyclooctadiene)₂ (Ni-(COD)₂ ; freshlyrecrystallized from toluene) was crushed with a mortar and pestle. Theyellow powder was suspended in approximately 20 ml of rapidly stirreddiethyl ether and then added in approximately 5 ml aliquots to 1.12(7.27 mmol) of allyl trifluoroacetate at 0° C. The resulting deep Redmixture was stirred for 11/2 hours at 0° C., or until all of the yellowNi(COD)₂ was consumed. The resulting clear red solution was thencannula-filtered through a plug of glass microfibre disk, andthree-quarters of the solvent was pumped off while the mixture remainedat 0° C. The resulting brown-red slurry was washed with 2×10 ml aliquotsof pentane at -78° C., the supernatant was drawn off to yield anorange-brown powder, which was dried in vacuo overnight at 0° C. (yield0.560 g; 72.4%).

Analysis: ¹ H NMR (C₆ H₆): 4.80-5.30 ppm (1H), 2.45 ppm (2H), 1.60-1.90ppm (2H).

Preparation of Cis-5,6-bis(trimethylsiloxy)-1,3-Cyclohexadiene

2.02 g (18.9 mmol) of cis-5,6-dihydroxy-1,3-cyclobutadiene and a fewgrains of 4-(N,N-dimethyl amino) pyridine (4-DMAP) were dissolved in amixture of approximately 80 ml of methylene chloride and 4.32 ml (52.0mmol) of pyridine. While rapidly stirring under argon with thetemperature moderated with a room temperature water bath, 4.27 g (39.0mmol) of trimethylchlorosilane, diluted with a few ml of methylenechloride, was added dropwise to the pale yellow solution. After stirringfor 11/2 hrs at room temperature, the resulting cloudy white suspensionwas diluted with 10 ml of pentane to completely precipitate out thepyridinium hydrochloride salts. The salts were removed by filtrationthrough a medium porosity frit. The solvent was removed from thefiltrate in vacuo to yield a pale yellow oil. Vacuum distillation of theoil in a short path distillation apparatus yielded 3.92 g (84.8%) of aviscous, colorless, clear liquid (bp: 47° C. at 2 μm Hg pressure). C₆ H₆(OTMS)₂ : ¹ H NMR (C₆ D₆): 5.73-5.88 ppm (4H); 4.12 ppm (2H); 0.14 ppm(18H).

Polymerizations and Copolymerizations ofCis-5,6-Dihydroxy-1,3-Cyclohexadiene Derivatives

Approximately 0.010 g (2.35×10⁻⁵ mol) of (ANiTFA)₂ was weighted out in avial in a drybox, and then dissolved in 2.3 ml of solvent to give aclear orange solution. This solution was passed through a 0.5 micronMillipore filter, and then injected into a 50 ml capacity, thick walledglass Schlenk bomb with a 8 mm Kontes valve. The appropriate amount ofliquid monomer was then passed through a plug of basic alumina and addedto the reaction vessel. In the case of the CHD homopolymerizations andcopolymerizations, about 470 to 480 equivalents of monomer to catalystwere added in total. For the TMS-CHD polymerizations, about 50 to 200equivalents were added. Solid monomers were added by a powder funnel,while liquid monomers were added by syringe or pipet in the drybox. Inthe case of copolymerizations, the more reactive monomer was alwaysadded before the less active one. The polymerization mixture wasdegassed by repeated freeze-pump-thaw cycles and then backfilled withargon. After heating in a 50° C. oil bath with rapid stirring for 24hours, the mixture was poured into about 30 to 50 ml of a solvent inwhich the polymer was insoluble (usually, methanol). The polymer wasisolated by suction filtration, redissolved in a minimum amount ofsolvent if possible, and then re-isolated by the same method. The finalproduct was dried in vacuo to yield a fine white powder. 1,4-PCHD (88.4%yield in o-dichlorobenzene); ¹ H NMR (C₆ D₆): 5.6-5.8 ppm (2H); 1.9-2.1ppm (2H); 1.4-1.7 ppm (4H).

Copolymers of Various Compositions of CHD and BMC-DHCD

¹ H NMR (CDCl₃): 5.4-5.9 ppm (olefinic protons); 3.6-3.9 ppm(methoxycarbonyl protons); 1.2-2.1 ppm (allylic and methylene protons).

Poly(TMS-CHD)

(93% yield with 1.5M TMS-CHD and monomer:catalyst ratio=80:1, inchlorobenzene)

¹ H NMR (C₆ D₆): 5.1-6.7 ppm (2H); 3.8-4.4 ppm (2H); 3.2-3.6 ppm (1H);2.4-2.9 ppm (1H); 0.0-0.8 ppm (18H).

    ______________________________________                                        Elemental Analysis:                                                                        Expected C 56.19  H 9.43 Si 21.90                                C.sub.12 H.sub.24 O.sub.2 Si.sub.2                                                         Actual   C 55.91  H 9.34 Si 22.21.                               ______________________________________                                    

Preparation of 1,4-Poly(cis-5,6-diacetoxy)-1,3-cyclohexadiene)

A 50 ml Schlenk flask with an 8 mm Kontes valve was charged with1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene) (149.5 mg;0.583 mmol) and anhydrous zinc chloride (167 mg; 1.23 mmol) in anitrogen-filled glove box. On a Schlenk line, dry, degassed diethylether (10 ml) was added via syringe under Ar flush to the reactionvessel. The mixture was stirred for 0.5 hr to completely dissolve theZnCl₂. Then, distilled and degassed acetyl chloride (350 μl; 6.19 mmol)was added via syringe as a neat liquid to the clear, colorless solutionunder Ar flush. The mixture immediately became cloudy, and a paleyellow, gelatinous solid gradually precipitated with stirring over an 18hr period. Subsequently, the reaction mixture was decanted into methanol(100 ml) to precipitate the polymer. A colorless powder was isolated byfiltration and washed with methanol (20 ml). Vacuum-drying of this solid(<10 μm Hg, 1 hr) afforded 87 mg (76% yield) of1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene). This polymer waspurified by dissolution in the minimal amount of dichloromethane,filtration, and re-precipitation into hexanes (100 ml). The resultingcolorless powder was dried in vacuo for 12 hr.

Analysis: ¹ H NMR (400 MHz, CDCl₃ : δ 5.88 (s,2H), 2.82 (s,2H), 2.07(s,2H), 2.07 (s,6H). ¹³ C NMR (100 MHz, CDCl₃): δ 170, 127, 71, 37,21.5. IR (KBr mull): cm⁻¹ 3037, 2932, 1746, 1644, 1434, 1372, 1240,1166, 1053, 1026, 928, 768.

Anhydrous ferric chloride (FeCl₃) can also be used in place of ZnCl₂under the same reaction conditions for the conversion of1,4-poly(cis-5,6-(trimethylsiloxy)-1,3-cyclohexadiene) to1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene). However, after the1,4-poly(TMS-CHD), FeCl₃, and acetyl chloride have been stirring indiethyl ether for 1/2 hr, the reaction mixture must be quenched inmethanol and worked up as in the ZnCl₂ case to prevent further reactionof the FeCl₃ with the 1,4-poly(DA-CHD) formed.

In addition, treatment of1,4-poly[cis-5,6-bis(tri-methylsiloxy)-1,3-cyclohexadiene] with twoequivalents of iodotrimethylsilane in dimethyl ether resulted in thequantitative displacement of the trimethylsiloxy group and formation ofa new polymeric material with the postulated structure 1. The furtherformation of this product, cis-1,4-poly(5,6-diiodo-1,3-cyclohexadiene),and its potential for conversion to poly(para-phenylene) are understudy. ##STR1##

Synthesis and Polymerization of 5-methyl-1,3-cyclohexadiene

12.5 g (0.130 moles) of (±)5-methyl-1,3-cyclohexadiene (99.7%, WileyOrganics) was dissolved in 30 ml of carbon tetrachloride and 1.5 ml ofabsolute ethanol in a 250 ml B14/20 3-neck round bottom flask. Under anargon flush, 18.00 g (0.113 moles) of bromine diluted with 15 ml of CCl₄was added dropwise to the reaction mixture at -5° C. At the end of theaddition, a simple distillation apparatus was attached and excessstarting olefin was distilled off at 103° C. The dark residue wasseparated by fractional distillation at 0.1 Torr. The product,1,2-dibromo-4-methyl cyclohexane, was collected at 50° to 51° C. in83.0% yield (24.02 g).

10.00 g (0.039 moles) of 1,2-dibromo-4-methylcyclohexane was addeddropwise to a mixture of sodium isopropoxide at 100° to 110° C. (Theisopropoxide mixture was made by adding 2.08 g of NaH to 11.7 ml of dryisopropanol and 19.5 ml of triethylene glycol dimethyl ether under anargon flush.) The low boiling fraction (product and isopropanol) wasisolated by distillation from the reaction mixture at 75° to 78° C.,using a dry ice/isopropanol cold trap. The isopropanol was removed bywashing the distillate with water and drying the organic layer overcalcium hydride. 0.60 g (16.34%) of a colorless, clear liquid wasisolated by vacuum transfer:

¹ H NMR (CDCl₃): 1.0 ppm (3H); 1.5-2.8 ppm (5H); 5.5-5.9 ppm (4H).

In the drybox, 0.025 g (5.8×10⁻⁵ moles) of (ANiTFA)₂ was weighed out ina vial and dissolved in 3.5 ml of o-dichlorobenzene. The orange solutionwas clarified by passing through a 0.5 micron Millipore filter into aSchlenk bomb. 0.400 g (4.25×10⁻³ mole) of 5-methyl-1,3-cyclohexadienewas passed through 0.5 cm of basic alumina in the dry box and wasinjected into the catalyst solution. The bomb was sealed up,freeze-pump-thawed three times, and filled with argon. Thepolymerization mixture was heated for 24 hours in a 50° C. oil bathbefore precipitating out the polymer by pouring the mixture into 40 mlof methanol. The resulting grey gum was redissolved in 20 ml of benzeneand re-precipitated into methanol after passing the solution through a0.5 micron Millipore filter. 0.132 g (33.0%) of a white, soluble powderwas isolated by suction filtration and dried under dynamic vacuum:

¹ H NMR (CDCl₃): 0.8-1.0 ppm (3H); 1.2-2.2 ppm (5H); 5.4-5.8 ppm (2H).

GPC: Mn=1406 (vs. polystyrene standards)

Mw=1628

PDI=1.16

XRD: no sharp lines→amorphous

DSC: stable up to ≈330° C., contrast to PCHD 320° C.

Neopentyl, and other substituted CHDs, are synthesized and polymerizedsimilarly. Because these alkyl-substituted PCHDs are soluble and havethe same thermal stability as the parent PCHD polymer, they are likelyto find use as inexpensive, high performance polymers, especially when asmall amount is copolymerized with normal CHD to make the PCHD soluble.

Preparation of Poly(cis-5,6-dihydroxy-1,3-cyclohexadiene)

A 250 ml Schlenk flask was charged with a 1.0M solution oftetrabutylammonium fluoride in THF (40 ml) and additional dry THF (20ml) via syringe under Ar flush. A solution ofpoly(cis-5,6-trimethylsiloxy-1,3-cyclohexadiene (1.52 g) in dry THF (20ml) was added dropwise over a period of 20 min to the rapidly stirredsolution of (Bu)₄ NF. A thick yellow gum precipitated from the reactionmixture. Rapid stirring was continued for 4 hr, then the product wasprecipitated by the addition of anhydrous methanol (20 ml). After 12 hr,a colorless solid was isolated by filtration and washed with methanol(40 ml). The colorless precipitate was dried under vacuum (10⁻⁴ mm Hg)for 12 hr.

Preparation of Poly(cis-5,6-diacetoxy-1,3-cyclohexadiene

Under Ar, a 100 ml Schlenk tube with a polytetrafluoroethylene valve wascharged with poly(cis-5,6-dihydroxy-1,3-cyclohexadiene) (553 mg). Drypyridine (6.0 ml) and distilled, degassed acetic anhydride (2.6 ml) wereadded sequentially as neat liquids via syringe to the reaction flaskunder Ar flush. The flask was tightly sealed and the mixture was heatedat 80° C. with stirring for 24 hr. The initial slurry of the reactantdissolved, affording a clear, pale yellow solution The mixture wascooled to ambient temperature and the volatiles were removed in vacuo.The remaining yellow, glassy liquid was dissolved in dichloromethane (50ml) and extracted sequentially with saturated aqueous NaHCO₃ (25 ml) andsaturated NaCl (25 ml) solutions. The organic phase was separated, driedover anhydrous Na₂ SO₄, and filtered. The clear, pale yellow filtratewas concentrated to 5 ml by rotary evaporation. The concentrate wasadded dropwise to stirred hexanes (150 ml) to precipitate the polymer.The pale yellow precipitate was isolated by filtration and washed withhexanes (2×30 ml). The colorless solid was dried under high vacuum (10⁻⁴mm Hg) for 12 hr. Yield: 93% based on starting 1,4-poly(TMS-CHD), overtwo steps.

Thus, there has been disclosed a process for the preparation of fullyacetylated 1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene) and forconverting the fully acetylated polymer to poly(para-phenylene) havingessentially 100% 1,4-linkages and essentially no 1,2-linkages. It willbe apparent to those skilled in the art that various modifications andchanges of an obvious nature may be made, and all such modifications andchanges are considered to fall within the scope of the invention, asdefined by the appended claims.

What is claimed is:
 1. A process for converting1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene) to1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene), comprising:(a) reactingsaid 1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene) withacetyl chloride; and (b) retreating with pyridine and eitheraceticanhydride or acetyl chloride to yield essentially 100% acetylated1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene).
 2. The process of claim1 wherein said 1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene)is mixed with diethyl ether and zinc chloride or ferric chloride priorto addition of said acetyl chloride in step (a).
 3. A process forpreparing fully acetylated1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene) from1,4-poly(cis-5,6-dihydroxy-1,3-cyclohexadiene) comprising treating withpyridine and either acetic anhydride or acetyl chloride to yield 100%acetylated 1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene).
 4. A processfor preparing poly(para-phenylene) having essentially 100% 1,4-linkagescomprising heating fully acetylated1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene).
 5. The process of claim4 wherein said fully acetylated1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene) is prepared by a processcomprising:(a) reacting1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene) with acetylchloride; and (b) treating with pyridine and either acetic anhydride oracetyl chloride to yield 100% acetylated1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene).
 6. The process of claim5 wherein said 1,4-poly(cis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene)is prepared by polymerizingcis-5,6-bis(trimethylsiloxy)-1,3-cyclohexadiene) in the presence of anickel II catalyst having an allyl group and a non-basicelectron-withdrawing ancillary ligand.
 7. The process of claim 6 whereinsaid nickel II catalyst is selected from the group consisting ofbis[(ally)trifluoroacetatonickel(II)],bis[(allyl)pentafluorophenoxynickel(II)], andbis[(allyl)iodonickel(II)].
 8. The process of claim 4 wherein saidheating is carried out at a temperature of about 300° to 340° C.
 9. Theprocess of claim 4 wherein said fully acetylated1,4-poly(cis-5,6-diacetoxy-1,3-cyclohexadiene) is prepared by a processcomprising treating 1,4-poly(cis-5,6-dihydroxy-1,3-cyclohexadiene) withpyridine and either acetic anhydride or acetyl chloride.